Describe Your Changes

Tool-call parameter previews were unusable for file writes (and any tool with a
chunky text parameter): the input renders as one JSON.stringify line, so the
content string's newlines become literal \n escapes inside a single endless
line, and the scroll box stays pinned to the top while the input streams, so
you can't watch what's being generated.

Two changes in ToolInput:

• Multiline params become real text blocks. Top-level string parameters
  containing newlines (or ≥400 chars) are pulled out of the JSON preview and
  each rendered as its own labeled block with real newlines; the highlight
  language is guessed from a path-like sibling parameter (path,
  file_path, …). Remaining parameters stay as compact JSON. Inputs without
  such parameters render exactly as before, so small tool calls are
  unaffected.
• Streaming previews stay highlighted and follow the tail. Highlighting
  runs throughout the write, self-paced so a new pass starts only once the
  previous one finishes against the newest value (rendering every queued
  result replays a backlog of stale frames; dropping any result that is no
  longer newest starves them all). Only a bounded window of trailing lines is
  highlighted while streaming, so the pass stays a fixed cost instead of
  growing with the file, with the complete document rendered once the write
  finishes. Following the tail uses the project's existing
  use-stick-to-bottom behaviour, so it eases rather than snapping and
  releases when the reader scrolls away.

The split/guess logic lives in lib/toolParamPreview.ts with unit tests
(multiline extraction, long-string extraction, non-object passthrough,
language guessing). Verified in a local dev build against the filesystem MCP's
write_file: content renders as real multi-line text and the block follows
the tail as it streams, collapsing to a highlighted code block when done.

Fixes Issues

• Closes Tool-call parameter previews: multiline content renders as one line and doesn't follow generation #188

Before/After

Before:

After:

Self Checklist

• Added relevant comments, esp in complex areas (why streaming skips highlighting, the pin/release scroll rule)
• Updated docs (for bug fixes / features): n/a
• Created issues for follow-up changes or refactoring needed: n/a